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Unread 01-20-2008, 05:33 PM   #1
Chuck
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Default Ham & CB Antennas

Found an article in the Nov 07 issue of QST comparing HF mobile antennas, 80 through 10 meters. The 10 meter ham band is right above the CB band, so this should apply to CB as well.

The article states that the maximum transmission power occurs from the antenna through the longest dimension of the vehicle. For the truck, with the antenna mounted on the driver's side several feet behind the door, the max direction was off the right front fender. For the car, with the antenna mounted to the center of the trunk, the max direction was straight through the front of the car (diagram attached). The ratio of max to min was 2.5 dB (1.78) for the truck and 2.0 dB (1.58) for the car.

Does anyone know if this also applies to VHF and UHF antennas?

Mobile Antenna Direction.jpg
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Unread 01-20-2008, 06:26 PM   #2
bulldog
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Dunno about that article, but from wheelign with folks with CB antennas mounted on different lcoation I found that the opposite seemed to be true for CB antennas than the article states.

On UHF/VHF would be interestign to see. However most folsk find that ham seems so much better than CB that it becomes somewhat of a moot point.

I still pefer roof mount, preferably center roof.
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Unread 01-20-2008, 09:46 PM   #3
expat
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The diagram explanation for the cb antenna is correct.

If you place the antenna on the rear left, the best recpetion and transmission will be towards the front right. The transmission to rear in this example would be less than optimal. It's all about ground plane.

However, if you mounted the antenna on the rear bumper of a truck you also loose some of that forward transmission and reception due to the rear glass and steel that will feedback into the antenna which in turn leads to incresaed SWR and therefore lower quality performance.

Andries is correct that the center of the roof is generally the best location.

As to Ham radios, basically the same thing applies although if you buy a load antenna, the ground plane is not such an issue.

The past weekend I used both cb and ham antennas off the front corners of bullbar and with a low SWR (finally!) on both, I had excellent performance.

I would maintain my Wilson 5000 magnetic cb antenna placed on the roof still outperforms my 4ft Firestick antenna off the bumper but its pretty negligable difference.

I'm also happy that my antennas are not on the roof anymore. Last weekends trail in Nevada, people were removing their roof top antenna due to the low trees. I had no issues. Same applies to Big Bear and more.
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